The present invention relates to an electrophotographic copier, and more specifically, to an apparatus in which: a document image is photoelectrically converted into image data; the image data is compression processed; the processed data is temporarily stored in a memory means and then read out; and the image is recorded according to the read-out image data.
The following recording apparatus in which: a document image is read out; the read-out image data is compression processed and stored in a memory; the stored image data is sequentially read out and an image is formed, instead of the image formation in which a document image is directly projected onto a photoreceptor of an image forming apparatus; and, when an insufficient memory capacity remains in the apparatus, image data storing in the memory is stopped, and an alarm is activated, is disclosed in Japanese Utility Model Open to Public Inspection No. 38462/1988.
When image data is written into an image data storing memory, the larger the data compression ratio is, the smaller the required memory capacity needs to be. However the reproduced image quality is proportionately deteriorated.
In contrast to this, the smaller the data compression ratio is, the larger the required memory capacity needs to be, although deterioration of the reproduced image quality is at a minimum.
The data memory capacity required for a single sheet of document differs greatly depending on the kind of image, for example, a photographic image or a character image. Accordingly, the required memory capacity can not be determined until the image is actually read. Normally, the data compression ratio in the memory apparatus is previously set such that the image quality is not adversely affected. However, since the memory capacity installed in this kind of recording apparatus is limited, it can not be avoided that the writable memory capacity may be reduced to zero at the time of image data writing in the memory, that is, when memory data overflows the memory capacity.
When memory data overflows, the structure disclosed in the foregoing Japanese Utility Model is adopted in the apparatus.
In this case, when the memory data overflow alarm is noted by the operator, he had to manually change the data compression ratio, and the order of documents to be read out was returned to the initial one so that the image data reading operation into the memory was repeated.
In cases where the number of document sheets is reduced and the image data reading operation into the memory is carried out again from the first when the memory data overflow occurred, the following operations are carried out. When the documents are single sided and are fed in such a manner that the image surfaces are right side up and the stacked documents are fed sequentially from the top to bottom, the number of document sheets can be reduced easily. However, when the documents are fed in such a manner that the image surfaces are right side down in single sided documents and the stacked documents are fed sequentially from the bottom to top, or when the documents are double sided, the number of the document sheets can not be reduced easily. In such cases, when the operations are not carefully performed, there is a possibility that pages are missed, or the documents are read in such a manner that the document sheets are out of sequence. Accordingly, a longer period of time is necessary for the re-arrangement of the copied sheets.
Further recently, there is a tendency that the following method of using an image recording apparatus is becoming popular in order to increase the productivity of copying operation. The method is that the process of reading a document and simultaneously storing the obtained image data in a memory and the process of reading a document and simultaneously making an copy by performing a image forming operation are parallelly executed. In this case, when the number of the copying set is one, the storing operation in the memory and the copying operation of the image data are completed immediately. When the number of the necessary copying sets is N (N is an integer not less than 2), the rest of the copying sets, the number of which is N-1, is provided by reading out the image data from the memory, in which the image data are already stored, and forming the image accordingly. When the aforementioned copying method is used, the recovery operation from memory overflow takes unexpected effort.